Internal micrometer

ABSTRACT

The present invention has for its object, an internal micrometer comprising a cylindrical body, a control shaft which is movable in a rotational and longitudinal manner within the body and two conical coaxial members connected to one another by a rod, driven by said shaft and controlling the movements of at least one measuring key movable perpendicularly to the shaft of said conical members.

United States Patent [191 [11] 3,721,012 Muller 51March 20, 1973 [s41INTERNAL MICROMETER 2,047,607 7/1936 Zimmerman ..33/17s R [75] Inventor:Albert Muller, Crissier, Switzerland Primary Examiner Leonard Forman 7[73] 'Assignee: Tesa S.A., Renes, Switzerland Assistant Examiner-A. J.Mirabito [22] 16 May 14 1970 Attorney'James M. Heilman and Heilman &Heilman PP 373193 [57] ABSTRACT The present invention has for itsobject, an internal said conical members.

[30] Foreign Application Priority Data May 16, 1969 Switzerland..746l/69 [52] us. c1. "tea/17s R [51] Int. Cl. ..G01b 3/46, GOlb 5/08[58] Field Of Search..33/l78 R, 164 C, 143 G, 147 K [561 V I ReferencesCited UNITED STATES PATENTS 2,604,703 7/1952 -Meyer ..33/l78 R 4 Claims,3 Drawing Figures Pmmgnmzo 1975* 3.721.012

Fig. 3

ALBERT MULLER A T TORNE Y.

INTERNAL MICROMETER Internal micrometers comprising a micrometer readingdrum rigidly connected to a shaft carrying a micrometer screw whichengages in a mounting and a coaxial member in the form of a cone or aconical heli coidal ramp on which are supported movable, radialcylindrical feelers, are known. In these instruments, the rotation ofthe reading drum causes the shaft to rotate and therefore also themicrometer screw which in turn ensures the longitudinal displacement ofthe shaft and drum. When the shaft is displaced longitudinally theconical member also moves and the feelers move radially closer to orfurther away from one another, these movements being proportional to thetravel of the shaft.

These instruments give excellent results but have the disadvantage thatthey cannot be used for the measurement of small diameter bores, such asbores of less than 6 mm. because the measuring head, ie the feelers, theconical member controlling them, the return means which maintain thefeelers against the conical member and the fitting which supports andguides said members, takes up too much space and its dimensions cannotbe reduced beyond certain limits.

With the aim of remedying these disadvantages and in order to permit themeasurement of small internal dimensions, the present invention has forits object, an internal micrometer comprising a body, a control shaftwhich is movable in a rotational and longitudinal manner within the bodyand two conical coaxial members connected to one another by a rod,driven by said shaft and controlling the movements of at least onemeasuring key movable perpendicularly to the shaft of said conicalmembers, characterized in that an arm is coupled to the body, that themeasuring key comprises an elongated core extending along the arm andguided by the latter over at least part of its length, carrying at oneof its ends a feeler for making contact with the inside surface of abore to be measured and at its other end a support member sliding inslots made respectively in the arm and the body, and that one of theconical members is located in the body and controls the movements of thesupport member carried by the core of the key, while the other conicalmember contacts the movements of another part of the key.

The attached drawing shows by way of example one embodiment of a deviceaccording to the invention.

FIG. 1 is a part sectional elevation;

FIG. 2 is an enlarged section on the line 1-1 of FIG. 1.

FIG. 3 is a side view of the body.

The internal micrometer shown comprises a body 1 in which is located ashaft 2 of which one end is rigidly connected to a graduated readingdrum (not shown) rotatably associated with the body 1. The shaft 2 has acoaxial micrometer screw 3 engaging a thread 4 cut in the body 1. Theother end of the shaft 2 is designed so as to form a coaxial, conical,helicoidal ramp 5 having the same pitch as the screw 3.

The body 1 is connected to a tubular arm 6 of which one end is freewhile the other end has a support 7 coupled to the body 1 against whichit is held by a retaining disk 8 fixed to the body 1 by screws 9.

In the tubular arm 6 is placed a rotatable rod 10 coaxial to the shaft 2and of which one end is connected to the small end of the conicalhelicoidal ramp 5. The other end of the rod 10 is located inside thetubular arm 6 and carries a conical and coaxial helicoidal ramp 11. Theramp 11 is arranged in the same direction 5 as the ramp 5 and the axialpitch and radial pitch of the two ramps are respectively identical.

The outer wall of the arm 6 is cut by three longitudinal grooves 12(FIG. 2) arranged at 120 to one another on the periphery of the arm 6,each of said grooves terminating at one of its ends in a radial slot 13made at the free end of the tubular arm 6 and at its other end in aradial slot 14 made in the support 7 and arranged so as to face a radialslot 15 made in the body 1.

In each of the grooves 12 there is disposed the elongated longitudinalcore 16 ofa movable key 17. One of the ends of the core 16 has a radialfeeler l8 which-is parallel to the axis of the rod 10 extending alongthe slot 13 of arm 6. The feeler includes a slider 19 supported on theramp 11. The other end of the core 16 has a radial support member 20located in the recess formed by the slots 14 and 15 of the support 7 andthe body 1. The support member 20 is held in its recess by the retainingdisk 8 and has a slider 21 supported on the ramp 5. Each of the supportmembers 20 is traversed by a transverse groove and a circular returnspring 22 placed in said grooves and consequently, surrounding themicrometer, ensures the radial return of the keys The micrometerdescribed functions as follows: when the reading drum is turned thelatter drives the shaft 2 and micrometer screw 3 which is longitudinallydisplaced in the instrument. The rotation and displacementof the shaft 2causes the simultaneous rotation and displacement of the ramp 5, the rod10 and the ramp 11. The sliders 19 and 21 of the keys 17 are sup,-ported onthe ramps 5 and 11 and the rotation and displacement of thelatter will thus cause radial displacement of the keys 17. Given thatramps 5 and 11 have identical axial pitch and radial pitch, the keys 17will move parallel to the axis of the rod 10 and therefore parallel tothe axis of the instrument. As the ramps 5 and 11 have the same pitch asthe micrometer screw 3, the radial displacement of the keys 17 andtherefore, their feelers 18 will be proportional to the displacement ofthe reading drum, the graduation of which will permit the direct readingof the measurement made by the feelers 18.

The micrometer described offers the advantage of permitting themeasurement of very small internal dimensions because the use of twoconical members of different dimensions to control the displacement ofthe contacts, the simplification of the guiding of the feelers due tothe overall guiding of the keys and the fact that the return of the keysis remote from the feelers permit a very considerable reduction in thedimensions of the different members forming the measuring head.

As the feelers are located at the end of the arm, internal dimensionmeasurements can be made to a certain depth, the latter being naturallya function of the length of the arm 6. As the spring 22 is placedbetween the, conical members 5 and 11, its action extends to the wholelength of the keys 17 of which the sliders 19 and 21 are constantly incontact with the ramps 11 and 5. There is therefore no irregularity inthe displacement of the keys and as they perform a translationalmovement perpendicular to the instrument axis, the mounting of thefeelers 18 remains constant and is not disturbed by the return spring.

Due to the space saving obtained it is possible to use three keys toobtain a greater measuring accuracy. This number is not, however,limitative and can be reduced or even increased.

The conical helicoidal ramps described can be replaced by smooth cones,the angles of which are selected so as to ensure a movement of thecontacts which is proportional to the graduated drum movement.

The micrometer described can be manufactured without difficulty indimensions permitting the measurement of internal dimensions well below6 mm. and its use permits real measurements to be made without anynecessity of using an auxiliary comparator.

It is possible to place the conical member 11 so that it extends beyondthe end of the arm 6, the feelers 18 also being placed beyond the end ofthe arm and supported on the conical member, guiding then being assuredsolely by the core 16 and the contact support member 20.

According to another variation the conical member 11 can be placed inthe arm 6 at a certain distance from the free end thereof, the feelers18 being arranged at the end of said arm. In this case, the conicalmember 1 1 cannot act directly on the feelers l8 and instead acts on thecore 16 of contact 17.

Finally, it is possible to place the conical member 11 in the arm 6,while the feelers 18 are placed in front of and outside thereof. In thiscase, once again the conical member 1 1 cannot act directly on thefeelers and its action is on the core of the key, the guiding of thefeelers being assured by the core and the support member of the keys.

I claim:

1. An internal micrometer comprising:

a. an elongated tubular arm for insertion into a hole to be measured,said arm formed with a plurality of longitudinal grooves, each of saidgrooves extending the length of said arm and terminating in a slot atone end, of each arm said arm terminating in a cylindrical body at theend, said body having radial slots a plurality of longitudinal elongatedmovable measuring keys, one positioned in each of the grooves in saidarm, each key having a radially extending feeler positioned in the slotadjacent to the end of the arm which is to be inserted into the hole,the other ends of the keys terminated by radial support memberspositioned in the slot in the cylindrical body;

. a return spring surrounding the support members for moving the supportmembers, the measuring keys, and the radial feelers toward a centralaxial position in the tubular arm;

. an axial rotatable rod positioned in the center of the tubular arm,terminated at one end by a helicoidal ramp in contact with the radialfeelers, and terminated at the other end by a similar helicoidal ramp incontact with the radial support members;

. a haft secured to the rotatable rod coupling the rod to a micrometerscrew and to a manual means for turning the rod.

2. A micrometer according to claim 1 wherein the return spring ispositioned on the measuring keys between the points of contact of thesupport member and radial feelers with the two ramps for providing forthe return of the keys towards the axis of the tubular arm.

3. A micrometer according to claim 1 wherein said return spring isformed in a helix and is positioned in a circumferential slot in saidsupport members.

4. A micrometer according to claim 1 wherein said micrometer screw issecured to a reading drum which includes graduations thereon forindicating the diameter of the measured hole.

a: a: a: 1: :r

1. An internal micrometer comprising: a. an elongated tubular arm forinsertion into a hole to be measured, said arm formed with a pluralityof longitudinal grooves, each of said grooves extending the length ofsaid arm and terminating in a slot at one end, of each arm said armterminating in a cylindrical body at the end, said body having radialslots b. a plurality of longitudinal elongated movable measuring keys,one positioned in each of the grooves in said arm, each key having aradially extending feeler positioned in the slot adjacent to the end ofthe arm which is to be inserted into the hole, the other ends of thekeys terminated by radial support members positioned in the slot in thecylindrical body; c. a return spring surrounding the support members formoving the support members, the measuring keys, and the radial feelerstoward a central axial position in the tubular arm; d. an axialrotatable rod positioned in the center of the tubular arm, terminated atone end by a helicoidal ramp in contact with the radial feelers, andterminated at the other end by a similar helicoidal ramp in contact withthe radial support members; and e. a shaft secured to the rotatable rodcoupling the rod to a micrometer screw and to a manual means for turningthe rod.
 2. A micrometer according to claim 1 wherein the return springis positioned on the measuring keys between the points of contact of thesupport member and radial feelers with the two ramps for providing forthe return of the keys towards the axis of the tubular arm.
 3. Amicrometer according to claim 1 wherein said return spring is formed ina helix and is positioned in a circumferential slot in said supportmembers.
 4. A micrometer according to claim 1 wherein said micrometerscrew is secured to a reading drum which includes graduations thereonfor indicating the diameter of the measured hole.